Fluorinated saturated alkyl and alkoxy ethers containing one or more terminal nitrogen-containing functional groups, in particular those selected from nitriles, thiocyanates, cyanates and azides are useful materials in the fluoropolymer industry.
Fluorinated saturated alkyl and alkoxy ethers containing terminal azides groups can be used as cross linker in the preparation of fluoroelastomers. Therefore, there is a need to provide simple and effective methods to provide saturated fluorinated alkyl or alkoxy ethers containing terminal azide groups.
Fluorinated alkyl and alkoxy ethers containing terminal cyanates, thiocyanate and, in particular, nitrile groups can be converted into terminal carboxylic acids by hydrolysis of the nitrile, cyanate or thiocyanate groups. Partially fluorinated alkoxy carboxylic aids have been proposed as alternative and more environmentally-friendly (more biodegradable) emulsifiers replacements for perfluorooctanoic acid (CF3(CF2)6COOH) and its salts, which have been commonly used as emulsifiers in the preparation of fluoropolymers by aqueous emulsion polymerization. Various methods for the preparation of partially fluorinated alkoxy carboxylic acids have been described, which, however, involve complex and cumbersome processes. For example, US Pat Appl. No. 2006/0281946, to Morita et al, describes partially fluorinated carboxylic acid emulsifiers of the general formula Rf1(OCH2CF2CF2)n1OCX1X2CF2(Rf2)n2COOM where Rf1 represents a straight or branched fluoroalkyl group containing 1 to 20 carbon atoms, Rf2 represents a straight or branched fluoroalkylene group containing 1 to 25 carbon atoms, n1 represents an integer of 0 to 3, n2 represents an integer of 0 or 1, X1 and X2 are the same or different and each represent H or F and M represents NH4 or a monovalent metal element. These acids were reported to be obtainable by a ring opening addition of tetrafluorooxetane to a fluorine-containing acid fluoride followed by the conversion of the acid fluoride to the carboxylic acid. Such reaction sequence involves various reaction steps and is therefore technically difficult costly. In another publication (US Pat. Appl. No 2007/0025902 to Hintzer et al), several fluorinated alkoxy carboxylic acid emulsifiers and several methods of their preparation are described. For example, fluorinated carboxylic acids of the general formula Rfa-(O)t—CHF—(CF2)—COOH, wherein Rfa represents a linear fully or partially fluorinated aliphatic group optionally interrupted by one or more oxygen atoms and t represents 1 or 0 were described to be obtainable by a free radical reaction of a fluorinated olefin of the formula Rfa-(O)t—CF═CF2 with methanol followed by oxidation of the reaction product using a suitable oxidizing agent. For the oxidation metal oxides, such as KMnO4, RuO4, OsO4 or chromium (VI) oxide were suggested. Preparing the carboxylic acids in an industrial scale using such agents leads to cost-intensive waste treatment for removing residues the oxidizing agents. Although the above described methods may be used to prepare partially fluorinated alkoxy carboxylic acids, the need exists for alternative methods, in particular for the large scale production of the acids. Desirably, such methods allow the preparation of such acids in a simple and/or cost-effective process.